How to Decide Between Open- and Closed-Cell Spray Foam

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Insulator’s Guide to Open Cell vs. Closed Cell Spray Foam

We know that spray foam insulation has become an increasingly popular choice for builders, contractors and homeowners due to its many benefits. These include the ability to get into hard-to-reach places, offering the most energy efficient option, and its environmental benefits over other insulation types. In addition to energy savings, spray foam offers enhanced indoor comfort, soundproofing, allergen and pest control, superior water sealant, mold prevention qualities and added structural integrity.

Whatever your reason for choosing spray foam insulation, you’re not done making decisions quite yet. Now you have to consider whether open cell vs. closed cell spray foam insulation is right for your application. There are several variables to consider in making this decision.

What Is the Difference Between Open-Cell and Closed-Cell Foam?

The difference between open cell vs. closed cell spray foam insulation has to do with the bubbles, or cells, that the foam is made of.

Open cell foam is made up of tiny cells that are not completely encapsulated (like a kitchen sponge). Open cells mean this spray foam insulation is softer and more flexible than closed cell foam and is more porous for water vapor. This is ideal for achieving better insulating properties (e.g. more energy efficient) than fiberglass or mineral wool and for soundproofing properties. Open cell has a higher vapor permeability, which means it transmits water vapor and reduces the condensation problems that can occur with seasonal changes in weather or from humid air in warmer climates.

Closed cell foam is made up of even smaller cells that are completely closed. Because the closed cells are pressed tightly together, things like air and moisture are unable to get inside. This makes closed cell foam more rigid vs. open cell spray foam insulation and makes it a good water vapor retarder.

“Where is open cell foam used?” you may be wondering, after already picking up on a few benefits of closed cell foam. There are actually instances where open cell would be a better option. Open cell is commonly used in milder, more humid climates. It is also a good option where sound control is desired or less efficient insulation (than closed cell) is sufficient. Importantly, unlike closed cell foam, open cell foam is not a strong water vapor barrier, so in many cases a moisture vapor retarder is needed to prevent condensation from interior air onto cold surfaces through the foam (such as the roof deck or exterior walls).

In addition to the initial differences between open cell vs. closed cell spray foam insulation when it comes to the cells, there are plenty more differences to consider. Let’s discuss some in detail:


Open cell foam typically has an R-value somewhere between 3.6-3.8 per inch range as air is the only insulating gas present. Closed cell spray foam insulation has a much higher R-value, typically 6-7 per inch, due to its retention of powerful insulating gasses like hydrofluoroolefins (HFOs). If you’re insulating a building in an area with extreme temperatures and high humidity, you’d want to choose closed cell spray foam insulation over open cell, especially for exterior applications. Although open cell foam can be less costly than closed cell foam, more may be needed to meet prescribed total R-value requirements, as well as installation of a moisture vapor retarder. Your professional spray foam contractor can help guide your choice for the best option.


As we mentioned earlier, closed cell spray foam is much more dense and rigid than open cell. Most open cell foam has a density of about .5 pounds per cubic foot, whereas closed cell foam has a density of about 1.75 or more.

Open Cell vs. Closed Cell Spray Foam: Other Things You Need to Know

Does Closed Cell Foam Block Sound?

One plus side of spray foam insulation that doesn’t have to do with the actual insulating aspect, is that it can work as a sound barrier. Open cell does a much better job of soundproofing vs. closed cell spray foam insulation. While both can do a sufficient job, open cell insulation does a better job because the low-density, open structure dissipates sound waves unlike the more dense and rigid closed cells.

Can You Spray Open Cell Over Closed Cell?

Yes. Some contractors choose to supplement their closed cell spray foam with a layer of open cell spray foam over it. This is fairly common, however you wouldn’t ever want to spray closed cell over open cell because moisture would get trapped, potentially causing condensation. It is true, in some cases to blend costs in order to meet a prescribed overall R value, or as in the case of the Baton Rouge case study, closed cell was used to reinforce elements of the roof assembly, overwhich the bulk of Open Cell foam was applied as the primary insulation.

Is Closed Cell Spray Foam Safe?

When choosing closed cell spray foam it is important to choose a reputable spray foam installer. Because of the chemical composition, there are required installation requirements. Closed cell spray foam is a safe alternative when all pre and post installation steps are taken. These steps include proper ventilation, proper PPE for installers, clean up before and after spraying and adhering to manufacturer’s reentry times for trade workers and home occupants. Assuming a professional contractor has cured your spray foam insulation, and proper ventilation measures were taken within the space it was applied, closed cell spray foam insulation should not offgas toxic fumes after 24 hours.

Choose Natural Polymers for Your Open- and Closed-Cell Spray Foam

Now that you can answer the question, “What is the difference between closed cell foam and open cell foam?” you should feel better equipped to decide which is right for your application. Whichever type of foam you choose, Natural Polymers has the spray foam that will help you get the job done. Browse open cell and closed cell products we carry, or get in touch with us today.